Co-Site Interference Study and Mitigation Onboard a Submarine Between Communication and Positioning Systems at L Band

Abstract

This letter focuses on modeling and studying the RF interference between a civilian Inmarsat FB emitter at 1627 MHz (culprit) and a GPS L1 band maritime system at 1575 MHz (victim) on close antennas proximity onboard a submarine. Once predicted the RFI, we propose the design of an adequate mitigation for it. The chosen platform to host this study is a 3D model of the U.S. Navy retired Los Angeles SSN-688 original class submarine. The proposed methodology consists on calculating through numerical 3D electromagnetic simulation the electromagnetic decoupling between culprit and victim’s antennas on different antenna placement scenarios onboard the SSN-688’s masts; modeling a typical GPS front-end receiver simultaneously excited with both the interferer signal after decoupling, and the GPS weak signal reception; to observe the RFI effects on the modeled receiver circuit; and to finally propose and design an adequate filter to control and mitigate the interference. The result is a pre-filter, to be connected to the GPS receiver front-end before the GPS’s low noise amplifier, which attenuates the Inmarsat signal on the rejection band below the RFI threshold level and inserts a low insertion loss on GPS pass band.